1. Field of the Invention
The present invention relates generally to the fields of cell physiology, neurology, developmental biology, and oncology. More specifically, the present invention relates to novel methods of using a chlorotoxin sensitive cytoplasmic protein for the diagnosis and treatment of primitive neuroectodermal tumors (PNET).
2. Description of the Related Art
During embryonic development, the future nervous system forms from a specialized layer of ectodermal cells called the neuroectoderm. This layer extends longitudinally along the body axis congruent with the future spinal column. Invagination of the neuroectoderm gives rise to the neural tube from which essentially all central nervous system (CNS) components including the spinal cord develop. Specialized cell clusters along the rim of the invaginating neural tube stay separate from the tube and from the neural crest. These highly migratory neuroectodermal cells give rise to specialized cells throughout the body including Schwann cells, neuronal cells of the peripheral nervous system (PNS) (enteric, parasympathetic, sympathoadrenal, and sensory neurons), pigment cells (melanocytes), endocrine cells and cells forming connective tissue of the face and neck. Since these cells share a common embryonic origin with central nervous system cells, it is not surprising that these cells, or the tumors developing from these cells, share some genetic and antigenic phenotypes with central nervous system cells.
For example, melanomas and glioblastomas share a common mutation in the gene encoding for the epidermal growth factor receptor (EGFR) (1). Malignant astrocytomas and neurofibromas not only express high levels of the epidermal growth factor receptors but also vascular endothelial growth factor receptor (VEGF-R) and platelet-derived growth factor receptor (PDGF-R) (2). A high expression of the mutant variant, EGFRvIII, has been demonstrated in glial tumors as well as the extracellular matrix proteins, GP 240 and tenascin (3). Tenascin and the ganglioside-3′,6′-isoLD1 have been found in both gliomas and primitive neuroectodermal tumor tissues (3). In another study, antibodies to tenascin bound extensively to CNS gliomas and also to melanomas, breast, lung and squamous cell carcinomas (4). Another ganglioside, GD2, has been shown to be a common antigen marker in both gliomas and primitive neuroectodermal tumor tissues (5). Other common antigens between melanomas and gliomas were demonstrated by showing that Tyr, TRP-1, TRP-2 and gp100 gene products are commonly found in both melanoma and glioma tumors (6). Common cytokines or their receptors linking tumors of astrocytomas, ependymomas and primitive neuroectodermal tumors have been identified as: interleukin (IL) IL-1 alpha, IL-1, IL-1R1, IL-1R antagonist and transforming growth factor (TGF) TGF-beta 1 (11).
Another class of proteins used as markers for gliomas and primitive neuroectodermal tumors are the cytoskeletal proteins, neurofilament (NF), glial fibrillary acidic protein (GFAP), intermediate filaments (IF), intermediate associated protein filament (IFAP), vimentin, nestin and keratins. These markers have been used to determine stages of differentiation along the various cell lineages (12). New evidence linking astrocytomas with certain primitive neuroectodermal tumor tumors is the cytoskeleton marker of IFAP-300 kDa, a marker of immature glia (13).
Further arguments for a tight linkage of neuroectodermally derived cells in the central nervous system and periphery can be made based on their similar dependence on epigenetic influences. For example, sympathoadrenal precursor neurons require basic fibroblast growth factor (bFGF) to proliferate and differentiate, but survival of these cells depends on nerve growth factor (NGF) responsiveness and nerve growth factor availability (14). A similar scenario is required for each of the other cell types. Not only are growth and trophic factors necessary but cytokines and hormones are needed for which links remain to be elucidated between primitive neuroectodermal tumors and gliomas.
However, despite this list of similarities shared between neuroectodermally derived cells, these cells are distinct entities with unique cytological, biochemical and functional features. Indeed, the list of unique features not shared with other neuroectodermally derived cells by far exceeds the above mentioned shared phenotypes. Thus, one can not assume a priori that expression of a certain antigen or phenotype is to be expected in a given cell type based on expression by any other member of the neuroectodermally derived cell types.
Neuroblastomas generally express a selective increase in the gene copy number of the MYCN gene found in fetal stages of brain development suggesting links between the origin of the cells and the ability of neoplastic cells to dedifferentiate (7). However, this gene has yet to be demonstrated in the glioma cells. Other proteins that are not common to both glioma and primitive neuroectodermal tumors have been demonstrated. CD99 immunoreactivity is used as a tool in identifying primitive neuroectodermal tumors (8) and has been shown in Ewing's sarcoma tumors although not in gliomas (9). Another factor, stem cell factor and its receptor, c-kit, are also expressed in both primitive neuroectodermal tumor and Ewing's Sarcoma tumors (10).
The common origin and ability to respond to internal and external signals during the normal developmental processes suggests that central nervous system cells and peripheral neuroectodermally derived cells may also share common mechanisms during pathological developments as for example, during neoplasia. Such neoplastic tissues include CNS gliomas that are glial-derived tumor cells specific to the CNS. They metastasize only within the CNS including the spinal column. They are believed to originate from at least three separate lineages either from undifferentiated precursor cells or by dedifferentiation of astrocytes, oligodendrocytes or ependymal cells.
Primitive neuroectodermal tumors (PNET) are found both in the CNS and PNS. Primitive neuroectodermal tumors found only in the PNS are referred to as peripheral primitive neuroectodermal tumors (PPNET). Primitive neuroectodermal tumors manifest preferentially in children and have capacity for developing into a variety of neuronal, astrocytic, ependymal, muscular and melanotic lines. The conceptual basis of grouping these tumors together is based upon sharing common progenitor cells as well as sharing similar neoplastic transformations leading to tumors of similar morphological features and biological behavior. However, there remains controversy in placing all primitive neuroectodermal tumors into the same categories. The following paragraphs demonstrate examples of the overlap of common antigens between the various types of CNS and PNS tumors.
Supratentorial primitive neuroectodermal tumors include cerebral medulloblastomas, cerebral neuroblastomas, ‘blue’ tumors, ependymoblastoma and other primitive neuroectodermal tumors, such as pineoblastomas (WHO grade IV). The most useful markers for these tumors include GFAP, NFP, desmin and melanin. Others antigens found in these tumors are vimentin, nestin, keratin but are not useful for diagnostic purposes.
Peripheral neuroblastic tumors of the adrenal gland (medulla) and sympathetic nervous system are the most common type of childhood tumor outside of the CNS. Primary sites for these primitive neuroectodermal tumors are in the adrenals, abdominal, thoracic, cervical and pelvic sympathetic ganglia but include other primary sites as orbit, kidney, lung, skin, ovary, spermatic cord, and urinary bladder. Specific names of these related tumors are pheochromocytomas, paraganglioma, neuroblastomas, ganglioneuromas, ganglioneuroblastomas, neurofibromas, schwannomas, and malignant peripheral nerve sheath tumors. These all share common origin in the neural crest. Neuroblastomas all share high TRK-A (NGFR) and CD44 expressions. Neuronal specific enolase (NSE), synaptophysin, neural filament (NF) protein, GD2, tyrosine hydroxylase (TH) and chromogranin are used as diagnostic markers also found in medulloblastomas. Neuroblastomas generally express a selective increase in the gene copy number of the MYCN gene found in fetal stages of brain development (7).
Medulloblastomas are members of the primitive neuroectodermal tumors that are described as highly malignant embryonal tumors of the CNS found in the cerebellum (WHO grade IV). A common antigen of these medulloblastoma and other neuronal lineage tumors is synaptophysin (not found in glial or mesenchymal brain tumors). Nestin (IF protein) is found in developing CNS precursor cells and in medulloblastomas and in some peripheral neuroectodermal origin cells. Nestin (and vimentin) are found in medulloblastomas, astrocytomas, glioblastomas, ependymomas, gangliogliomas and meningiomas (only GFAP is found in the astrocytic-derived cells, which are occasionally ‘trapped’ in medulloblastomas). Increased levels of neural-cellular adhesion molecule (N-CAM) found in these tumors, may reflect levels of differentiation in the development of tumors (15). While varying levels of nerve growth factor (NGF), are found in nearly all tumors, medulloblastomas exhibited substantial reactivity to the NGF receptor and related proteins, neurotrophin (NT) NT-3, TRK-C and brain derived neurotrophic factor (BDNF) (16).
Melanomas, arising from melanocytes follow a graded development from diffuse melanocytosis, to melanocytoma to malignant melanomas. S100 protein is a marker for these tumors, as vimentin and NSE reactivity are variable.
Small cell neuroendocrine carcinomas of the lung are highly invasive and typically found in adult smokers. They have been shown to exhibit reactivity to many of the neural and neuroendocrine markers (some of them similar to N-CAMs) for tumor differentiation as peripheral primitive neuroectodermal tumors, gliomas, and ependymomas. These markers include neural specific enolase and extremely high c-src expression (17).
A feature conspicuously shared between developing CNS cells and neural crest derived cells is their propensity to migrate either towards a target or target area. It is believed that this ability is lost after cell differentiation and maturation. However, tumors of the CNS show significant cell migration and invasion into healthy brain, suggesting that cell have maintained or regained this enhanced migratory ability. It is, thus, not surprising that neoplastic transformation of neuroectodermally derived cells outside the CNS would have similar migratory abilities. At the intended destination, these cells differentiate into their final phenotype, similar to normal development, influenced by several trophic factors crucial for the proliferation and differentiation of various cell types.
The prior art is deficient in the lack of an diagnostic and therapeutic agents specifically targeted to primitive neuroectodermal tumors. The present invention fulfills this longstanding need and desire in the art.